For some time it has been recognized that the femur axial force measurement required by Federal Motor Vehicle Safety Standards (Occupant Crash Protection) did not necessarily reflect the true injury potential to a front seated vehicle passenger's legs during a crash test. In 1975, a report was presented at the 19th Stapp Car Crash Conference by R. P. Daniel, the inventor of the force-indicating dummy legs embodying the present invention, and Messrs. K. R. Trosien and B. O. Young. The report, entitled "The Impact Behavior of the Hybrid II Dummy" (Proceedings of the 19th Stapp Car Crash Conference, 1975, pp. 117-137), disclosed that femur bending and torsional moments can be major loading mechanisms during sled or vehicle crash tests. Several attempts at strain gaging the tibia to measure some of these loading mechanisms were without much success.
The consideration of particularly two-point harness/knee bolster passive restraint systems to meet the requirements of Federal Motor Vehicle Safety Standard 208 led to the need to accurately and reliably measure these and other leg loads. Such systems are likely to impose considerable and varied loading on the legs in forward crash situations, depending upon the bolster's size, shape, location, and energy absorbing and knee pocketing characteristics.
In 1978 and 1979, two events took place which made the development of force indicating legs possible. First, a paper was presented which described the mechanism of the human knee joint and gave tentative load deflection values for the joint up to rupture of the posterior cruciate ligament. This paper, by D. C. Viano et al, was entitled "Bolster Impacts to the Knee and Tibia of Human Cadavers and an Anthropomorphic Dummy" (Proceedings of the 22nd Stapp Car Crash Conference, 1978, pp. 403-428). Secondly, six-axis femur and tibia load cells were developed which provided accurate, compact, and replaceable load and moment measuring capability.
Several requirements were identified for the force indicating legs. It was believed necessary that the final design should:
1. Be capable of measuring tibia and femur (a) axial (tension/compression) loads, (b) shear loads in both orthogonal axes, (c) bending moments in both planes, and (d) torsional moments about the longitudinal axes. PA1 2. Be capable of measuring tibia-to-femur (knee joint) shear loads. PA1 3. Have knee joint load deflection capability. PA1 4. Have a more human-like knee joint contact area. PA1 5. Reduce the skeletal-to-flesh weight ratio of the current dummy legs. PA1 6. Be adaptable to other size dummies. PA1 7. Measure the ankle joint upward loading. PA1 8. Be durable, reliable and easy to use.